A seal ring is mounted in an annular groove formed in a peripheral surface of one of two members (shaft member and housing) which rotate relative to each other. The seal ring is brought into close contact with a side wall surface of the annular groove and a peripheral surface of another of the two members so as to be freely slidable, to thereby seal an annular gap formed between the two members. The seal ring is used for apparatus using a fluid pressure of hydraulic working oil (hereinafter abbreviated as “working oil”) or the like, which include an automatic transmission (hereinafter referred to as “AT”) and a continuously variable transmission (hereinafter referred to as “CVT”) for an automobile.
Various seal rings have been proposed as the above-mentioned seal ring. For example, in Patent Literature 1, there is proposed a seal ring having features (1) to (5) described below for the purpose of reducing a sliding resistance and improving ease of assembly.
(1) The seal ring includes a first sealing portion configured to seal a side wall surface of an annular groove, which is formed in one of two members, on a side not closer to a fluid to be sealed (low-pressure side).
(2) The seal ring includes a second sealing portion configured to seal a surface of another of the two members.
(3) The seal ring has a structure in which an axial width of a ring main body on a side closer to a groove bottom of the annular groove than to the first sealing portion is set smaller than an axial width of the ring main body at the first sealing portion.
(4) The seal ring has a structure in which projecting portions projecting toward side wall surfaces of the annular groove are formed over an entire periphery on the side closer to the groove bottom than to the first sealing portion.
(5) The projecting portions are formed so as not to come into contact with the side wall surfaces of the annular groove even when a fluid to be sealed acts in an annular gap formed between the two members.
Further, in Patent Literature 2, there is proposed a seal ring having features (1) to (4) described below for the purpose of achieving reduction in heat generation amount and achieving reduction in contact pressure.
(1) Side surfaces of the seal ring, which are opposed to side wall surfaces of an annular groove, are formed of level-difference surfaces which are recessed on a side closer to a groove bottom of the annular groove so as to be apart from the side wall surfaces.
(2) A plurality of projections which project toward the side wall surfaces are independently formed on the recessed surfaces.
(3) One of side surfaces of the seal ring, which is closer to another member, is brought into close contact with the side wall surface of the annular groove so as to be freely slidable, thereby forming a seal.
(4) Distal end surfaces of the plurality of projections are brought into close contact with the side wall surface of the annular groove so as to be freely slidable.